FIG. 4 is a block diagram showing a general configuration example of a mobile communications system. In FIG. 4, nodes having nothing to do with the Background Art section, and nodes unnecessary for explanation are omitted. In FIG. 4, a core network 10 is managed by an operator that mainly provides mobile communication services. The core network 10 is, for example, a packet switching network (EPC (Evolved Packet Core)) of an EPS (Evolved Packet System) or a packet switching core network of a UMTS (Universal Mode Telecommunications System) of the 3GPP, a packet switching core network of CDMA2000 of the 3GGP2, or a packet switching core network of a CSN (Connectivity Service Network) of the WiMAX Forum.
A radio access network 20 includes a radio base station 910 and a mobile terminal 930. The radio base station 910 has a function of connecting to the mobile terminal 930 by a radio access technique. The core network 10 includes a mobility management node 200. The mobility management node 920 performs mobility management and authentication (security control) of the terminal 930 during radio access, and manages setting processes and control signals for a user data transfer path between the core network 10 and the radio base station 910. The mobile terminal 930 has a radio interface, and connects to the radio base station 910 by the radio access technique and also connects to the core network 10.
In the EPS of the 3GPP, the radio base station 910 corresponds to an eNB (Enhanced NodeB); the mobility management node 920 corresponds to an MME (Mobility Management Entity); and the mobile terminal 930 corresponds to a UE (User Equipment). As the radio access technique, LTE (Long Term Evolution) is employed.
In the UMTS of the 3GPP, the radio base station 910 corresponds to functions of an RNC (Radio Network Controller) and an NB (NodeB). The mobility management node 200 corresponds to an SGSN (Serving GPRS Support Node), and the mobile terminal 300 corresponds to the UE (User Equipment). As the radio access technique, W-CDMA (Wideband Code Division Multiple Access) is employed.
In the CDMA2000 system of the 3GGP2, the radio base station 100 corresponds to a BS (Base Station); the mobility management node 200 corresponds to a PDNS (Packet Data Serving Node); and the mobile terminal 300 corresponds to an MS (Mobile Station). As the radio access technique, EV-DO (Evolution-Data Optimized) is employed.
In a communication system of the WiMAX Forum, the radio base station 100 corresponds to functions of an ASN-GW (Access Service Network Gateway) and the BS (Base Station). The mobility management node 200 corresponds to an HA (Home Agent), and the mobile terminal 300 corresponds to an MS (Mobile Station). As the radio access technique, WiMAX is employed.
Aspects and embodiments of the present invention herein described are not dependent on architectures of mobile communications systems. Accordingly, aspects and embodiments of the present invention can be applied to mobile communications systems standardized in the 3GPP, 3GPP2, and WiMAX Forum. However, the following description will be made with reference to the mobile communications system of the EPS in the 3GPP so as to describe configurations and operations according to aspects and embodiments of the present invention in detail.
In FIG. 31, a radio control including allocation of resources (channels) in a radio section between the mobile terminal 930 and the radio base station 910 is carried out in an RRC (Radio Resource Control) layer, and exchange of control messages and packet communication between the mobile terminal 300 and the core network 10, for example, are carried out in a NAS (Non-Access Stratum) layer which is upper layer of the RRC.
In RRC layer, there are two states of RRC_IDLE and RRC_CONNECTED. In the RRC_CONNECTED state, the radio base station 910 holds information (i.e., RRC context) on an RRC connection between the mobile terminal 930 and the radio base station 910, and transmission and reception of user data in the radio section between the mobile terminal 930 and the radio base station 910 are thereby enabled. On the other hand, in the RRC_IDLE state, the radio base station 100 releases the information (RRC context) on the RRC connection of the mobile terminal 300, discontinuous reception (DRX) that is configured by NAS is indicated to the mobile terminal 300, and therefore the mobile terminal 300 is able to receive a paging signal.
During the discontinuous reception, a radio communication unit included in the mobile terminal 930 is activated to perform a reception operation in accordance with time slots to be received by the mobile terminal 930. During the other time periods, the radio communication unit is brought into a standby state (power-off). Thus, the discontinuous reception provides a great effect of power saving in the mobile terminal 930.
In the NAS layer, there are two states of ECM (EPS Connection Management)_IDLE and ECM_CONNECTED. In the ECM-CONNECTED state, a NAS connection is established between the mobile terminal 930 and the mobility management node 920. The mobility management node 920 accurately recognizes the position of the mobile terminal 930 (i.e., recognizes a radio base station to which the mobile terminal is connected) by using the NAS connection, and performs a handover process when the mobile terminal 930 moves between base stations. On the other hand, the ECM_IDLE state is a state in which the NAS connection is not established between the mobile terminal 930 and the mobility management node 920. In the ECM_IDLE state, the mobility management node 920 performs mobility management of the mobile terminal 930 in units of tracking areas that each includes a plurality of radio base stations. Accordingly, even when the mobile terminal 930 in the ECM_IDLE state moves between radio base stations, no handover process occurs. When the mobile terminal 930 returns to the ECM_CONNECTED state from the ECM_IDLE state, the mobile terminal 930 needs to be synchronized with the core network 10 (i.e., needs to perform location registration).
When the mobile terminal 930 is in ECM_IDLE state and the mobility management node 920 performs the mobility management of the mobile terminal 930 in units of tracking areas, there is no need to perform the handover process even when the mobile terminal 930 moves between radio base stations. This provides an advantage of reducing a load on the core network (including the mobility management node 200).
It can be said that the states (CONNECTED or IDLE) related to connections of the RRC layer and the NAS layer are synchronized. This is because it is necessary to establish a connection in the RRC layer (come into the RRC_CONNECTED state) so as to establish a connection in the NAS layer (come into the ECM_CONNECTED state), and the connection in the NAS layer is established simultaneously with the establishment of the connection in the RRC layer. This is also because when the connection in one of the RRC layer and the NAS layer is released (transits to the IDLE state), the connection in the other layer is also released (transits to the IDLE state).
When the NAS layer transits from the ECM_CONNECTED state to the ECM_IDLE state, an S1 Release Procedure is executed. As an example of a trigger for executing the S1 Release Procedure is a release of RRC-connection (a transition to RRC_IDLE state). When the S1 Release Procedure is executed in the state where the connection in the RRC layer is established (RRC_CONNECTION state), the connection in the RRC layer is also released (transits to RRC_IDLE). That is, when the RRC layer and the NAS layer transit to the IDLE state, the S1 Release Procedure is executed.
On the other hand, when the RRC layer and the NAS layer transit to the CONNECTED state from the IDLE state, a Service Request Procedure is executed. When the Service Request Procedure is executed, the NAS connection and the RRC connection are established.
Here, the definition of terms “CONNECTED state” and “IDLE state” which are used in this specification and the claims is described. The term “IDLE state” refers to a state in which a mobile terminal does not perform signaling for session management and mobility management with a core network, and radio resources in a radio access network such as E-UTRAN are released, as in the case of the ECM_IDLE state and the RRC_IDLE state of the 3GPP described above. On the other hand, the term “CONNECTED state” refers to a state in which radio resources for sending and receiving control signals (control messages) for at least session management and mobility management between a mobile terminal and a core network are secured in a radio access network, and the control signals (control messages) can be sent and received between the mobile terminal and the core network, as in the case of the ECM_CONNECTED state and the RRC_CONNECTED state of the 3GPP described above. That is, it is only necessary that the “CONNECTED state” is a state in which a mobile terminal is connected to a core network so as to enable transmission and reception of control signals (control messages) for at least session management and mobility management. In other words, the “CONNECTED state” does not require a state in which a bearer for transferring user data between a mobile terminal and an external packet data network (PDN) is established.